Hepatocellular carcinoma (HCC) is one of the commonest cancers in the world with a less than 5% cure rate. The long-term goal of this proposal is to develop better treatment regimens for HCC through an improved understanding of its chemoresistant properties. In a recent pilot study conducted in this institution, 20 patients with Stage II-IVA non-resectable HCC were treated with orthotopic liver transplantation (OLT) and neoadjuvant low dose doxorubicin chemotherapy. The 3 year tumor-free survival rate of 54% was significantly better than the expected overall survival rate of 18% by OLT alone. These observations suggest that the neoadjuvant doxorubicin chemotherapy favorably alters the post-transplant survival Of HCC patients. OLT-transplanted HCC patients routinely received post-transplant immunosuppressive doses of' cyclosporin A (CSA), which was shown recently to exhibit chemosensitizing properties in reversing thee function of the P-glycoprotein (Pgp), a product of the multidrug resistant (MDR) gene. The Pgp presumably acts as an efflux pump in reducing the intracellular concentration of a variety of polycyclic anti-cancer drugs. Pgp, expressed intrinsically in normal hepatocytes and overexpressed in HCC, is likely to contribute to the commonly chemoresistant nature of HCC. The chemosensitizing effect of CSA is a likely explanation for the, improved response to doxorubicin. This proposal will examine the hypothesis that exposure to CSA enhances the chemotherapeutic efficacy of doxorubicin in HCC by modulating the cancer's MDR activity. Access to resected tissues of patients who undergo OLT and neoadjuvant doxorubicin therapy provides the opportunity to examine prospectively MDR gene activity in HCC, based on evaluations of Pgp and function. The specific aims for this proposal are: l) To document expression of Pgp and its mRNA in HCC and non-malignant liver tissues; 2) To characterize MDR activity by cytotoxicity and drug retention studies; and 3) To correlate CSA exposure with changes in Pgp expression and function. Observations from these studies will validate or refute the role of CSA in reversing doxorubicin chemoresistance in HCC. By providing a better understanding of the role of the MDR mechanism in HCC and a means of its circumvention, we hope to attain a scientific basis for designing further improvements for our ongoing Phase II and III trial of using neoadjuvant chemotherapy and liver transplantation for treatment of hepatocellular carcinoma.